dl-load.c

Newlib 嵌入式 C库 标准实现代码

      maplength = ehdr->e_phnum * sizeof (ElfW(Phdr));
      if (ehdr->e_phoff + maplength <= fbp->len)
	phdr = (void *) (fbp->buf + ehdr->e_phoff);
      else
	{
	  phdr = alloca (maplength);
	  lseek (fd, SEEK_SET, ehdr->e_phoff);
	  if (__libc_read (fd, (void *) phdr, maplength) != maplength)
	    {
	    read_error:
	      errval = errno;
	      errstring = N_("cannot read file data");
	      goto call_lose;
	    }
	}

      /* Check .note.ABI-tag if present.  */
      for (ph = phdr; ph < &phdr[ehdr->e_phnum]; ++ph)
	if (ph->p_type == PT_NOTE && ph->p_filesz == 32 && ph->p_align >= 4)
	  {
	    if (ph->p_offset + 32 <= fbp->len)
	      abi_note = (void *) (fbp->buf + ph->p_offset);
	    else
	      {
		lseek (fd, SEEK_SET, ph->p_offset);
		if (__libc_read (fd, (void *) abi_note_buf, 32) != 32)
		  goto read_error;

		abi_note = abi_note_buf;
	      }

	    if (memcmp (abi_note, &expected_note, sizeof (expected_note)))
	      continue;

	    osversion = (abi_note[5] & 0xff) * 65536
			+ (abi_note[6] & 0xff) * 256
			+ (abi_note[7] & 0xff);
	    if (abi_note[4] != __ABI_TAG_OS
		|| (_dl_osversion && _dl_osversion < osversion))
	      {
	      close_and_out:
		close (fd);
		__set_errno (ENOENT);
		fd = -1;
	      }

	    break;
	  }
    }

  return fd;
}

/* Try to open NAME in one of the directories in *DIRSP.
   Return the fd, or -1.  If successful, fill in *REALNAME
   with the malloc'd full directory name.  If it turns out
   that none of the directories in *DIRSP exists, *DIRSP is
   replaced with (void *) -1, and the old value is free()d
   if MAY_FREE_DIRS is true.  */

static int
open_path (const char *name, size_t namelen, int preloaded,
	   struct r_search_path_struct *sps, char **realname,
	   struct filebuf *fbp)
{
  struct r_search_path_elem **dirs = sps->dirs;
  char *buf;
  int fd = -1;
  const char *current_what = NULL;
  int any = 0;

  buf = alloca (max_dirnamelen + max_capstrlen + namelen);
  do
    {
      struct r_search_path_elem *this_dir = *dirs;
      size_t buflen = 0;
      size_t cnt;
      char *edp;
      int here_any = 0;
      int err;

      /* If we are debugging the search for libraries print the path
	 now if it hasn't happened now.  */
      if (__builtin_expect (_dl_debug_mask & DL_DEBUG_LIBS, 0)
	  && current_what != this_dir->what)
	{
	  current_what = this_dir->what;
	  print_search_path (dirs, current_what, this_dir->where);
	}

      edp = (char *) (memcpy (buf, this_dir->dirname, this_dir->dirnamelen) + this_dir->dirnamelen);
      for (cnt = 0; fd == -1 && cnt < ncapstr; ++cnt)
	{
          char *tmp;
	  /* Skip this directory if we know it does not exist.  */
	  if (this_dir->status[cnt] == nonexisting)
	    continue;

          tmp = memcpy (edp, capstr[cnt].str, capstr[cnt].len);
          tmp += capstr[cnt].len;

          tmp = memcpy (tmp, name, namelen);
          tmp += namelen;
	  buflen = ((char *) (tmp - buf));

	  /* Print name we try if this is wanted.  */
	  if (__builtin_expect (_dl_debug_mask & DL_DEBUG_LIBS, 0))
	    _dl_debug_printf ("  trying file=%s\n", buf);

	  fd = open_verify (buf, fbp);
	  if (this_dir->status[cnt] == unknown)
	    {
	      if (fd != -1)
		this_dir->status[cnt] = existing;
	      else
		{
		  /* We failed to open machine dependent library.  Let's
		     test whether there is any directory at all.  */
		  struct stat64 st;

		  buf[buflen - namelen - 1] = '\0';

		  if (stat64 (buf, &st) != 0
		      || ! S_ISDIR (st.st_mode))
		    /* The directory does not exist or it is no directory.  */
		    this_dir->status[cnt] = nonexisting;
		  else
		    this_dir->status[cnt] = existing;
		}
	    }

	  /* Remember whether we found any existing directory.  */
	  here_any |= this_dir->status[cnt] == existing;

	  if (fd != -1 && __builtin_expect (preloaded, 0)
	      && 0)
	    {
	      /* This is an extra security effort to make sure nobody can
		 preload broken shared objects which are in the trusted
		 directories and so exploit the bugs.  */
	      struct stat64 st;

	      if (fstat64 (fd, &st) != 0
		  || (st.st_mode & S_ISUID) == 0)
		{
		  /* The shared object cannot be tested for being SUID
		     or this bit is not set.  In this case we must not
		     use this object.  */
		  close (fd);
		  fd = -1;
		  /* We simply ignore the file, signal this by setting
		     the error value which would have been set by `open'.  */
		  errno = ENOENT;
		}
	    }
	}

      if (fd != -1)
	{
	  *realname = (char *) malloc (buflen);
	  if (*realname != NULL)
	    {
	      memcpy (*realname, buf, buflen);
	      return fd;
	    }
	  else
	    {
	      /* No memory for the name, we certainly won't be able
		 to load and link it.  */
	      close (fd);
	      return -1;
	    }
	}
      if (here_any && (err = errno) != ENOENT && err != EACCES)
	/* The file exists and is readable, but something went wrong.  */
	return -1;

      /* Remember whether we found anything.  */
      any |= here_any;
    }
  while (*++dirs != NULL);

  /* Remove the whole path if none of the directories exists.  */
  if (__builtin_expect (! any, 0))
    {
      /* Paths which were allocated using the minimal malloc() in ld.so
	 must not be freed using the general free() in libc.  */
      if (sps->malloced)
	free (sps->dirs);
      sps->dirs = (void *) -1;
    }

  return -1;
}

/* Map in the shared object file NAME.  */

struct link_map *
internal_function
_dl_map_object (struct link_map *loader, const char *name, int preloaded,
		int type, int trace_mode, int mode)
{
  int fd;
  char *realname;
  char *name_copy;
  struct link_map *l;
  struct filebuf fb;

  /* Look for this name among those already loaded.  */
  for (l = _dl_loaded; l; l = l->l_next)
    {
      /* If the requested name matches the soname of a loaded object,
	 use that object.  Elide this check for names that have not
	 yet been opened.  */
      if (__builtin_expect (l->l_faked, 0) != 0)
	continue;
      if (!_dl_name_match_p (name, l))
	{
	  const char *soname;

	  if (__builtin_expect (l->l_soname_added, 1)
	      || l->l_info[DT_SONAME] == NULL)
	    continue;

	  soname = ((const char *) D_PTR (l, l_info[DT_STRTAB])
		    + l->l_info[DT_SONAME]->d_un.d_val);
	  if (strcmp (name, soname) != 0)
	    continue;

	  /* We have a match on a new name -- cache it.  */
	  add_name_to_object (l, soname);
	  l->l_soname_added = 1;
	}

      /* We have a match.  */
      return l;
    }

  /* Display information if we are debugging.  */
  if (__builtin_expect (_dl_debug_mask & DL_DEBUG_FILES, 0) && loader != NULL)
    _dl_debug_printf ("\nfile=%s;  needed by %s\n", name,
		      loader->l_name[0] ? loader->l_name : _dl_argv[0]);

  if (strchr (name, '/') == NULL)
    {
      /* Search for NAME in several places.  */

      size_t namelen = strlen (name) + 1;

      if (__builtin_expect (_dl_debug_mask & DL_DEBUG_LIBS, 0))
	_dl_debug_printf ("find library=%s; searching\n", name);

      fd = -1;

      /* When the object has the RUNPATH information we don't use any
         RPATHs.  */
      if (loader == NULL || loader->l_info[DT_RUNPATH] == NULL)
	{
	  /* First try the DT_RPATH of the dependent object that caused NAME
	     to be loaded.  Then that object's dependent, and on up.  */
	  for (l = loader; fd == -1 && l; l = l->l_loader)
	    {
	      if (l->l_rpath_dirs.dirs == NULL)
		{
		  if (l->l_info[DT_RPATH] == NULL)
		    {
		      /* There is no path.  */
		      l->l_rpath_dirs.dirs = (void *) -1;
		      continue;
		    }
		  else
		    {
		      /* Make sure the cache information is available.  */
		      size_t ptrval = (D_PTR (l, l_info[DT_STRTAB])
				       + l->l_info[DT_RPATH]->d_un.d_val);
		      decompose_rpath (&l->l_rpath_dirs,
				       (const char *) ptrval, l, "RPATH");
		    }
		}

	      if (l->l_rpath_dirs.dirs != (void *) -1)
		fd = open_path (name, namelen, preloaded, &l->l_rpath_dirs,
				&realname, &fb);
	    }

	  /* If dynamically linked, try the DT_RPATH of the executable
             itself.  */
	  l = _dl_loaded;
	  if (fd == -1 && l && l->l_type != lt_loaded && l != loader
	      && l->l_rpath_dirs.dirs != (void *) -1)
	    fd = open_path (name, namelen, preloaded, &l->l_rpath_dirs,
			    &realname, &fb);
	}

      /* Try the LD_LIBRARY_PATH environment variable.  */
      if (fd == -1 && env_path_list.dirs != (void *) -1)
	fd = open_path (name, namelen, preloaded, &env_path_list,
			&realname, &fb);

      /* Look at the RUNPATH information for this binary.

	 Note that this is no real loop.  'while' is used only to enable
	 us to use 'break' instead of a 'goto' to jump to the end.  The
	 loop is always left after the first round.  */
      while (fd == -1 && loader != NULL
	     && loader->l_runpath_dirs.dirs != (void *) -1)
	{
	  if (loader->l_runpath_dirs.dirs == NULL)
	    {
	      if (loader->l_info[DT_RUNPATH] == NULL)
		{
		  /* No RUNPATH.  */
		  loader->l_runpath_dirs.dirs = (void *) -1;
		  break;
		}
	      else
		{
		  /* Make sure the cache information is available.  */
		  size_t ptrval = (D_PTR (loader, l_info[DT_STRTAB])
				   + loader->l_info[DT_RUNPATH]->d_un.d_val);
		  decompose_rpath (&loader->l_runpath_dirs,
				   (const char *) ptrval, loader, "RUNPATH");
		}
	    }

	  if (loader->l_runpath_dirs.dirs != (void *) -1)
	    fd = open_path (name, namelen, preloaded,
			    &loader->l_runpath_dirs, &realname, &fb);
	  break;
	}

      if (fd == -1
	  && (__builtin_expect (! preloaded, 1) || ! 0))
	{
	  /* Check the list of libraries in the file /etc/ld.so.cache,
	     for compatibility with Linux's ldconfig program.  */
	  const char *cached = _dl_load_cache_lookup (name);

	  if (cached != NULL)
	    {
#ifdef SHARED
	      l = loader ?: _dl_loaded;
#else
	      l = loader;
#endif

	      /* If the loader has the DF_1_NODEFLIB flag set we must not
		 use a cache entry from any of these directories.  */
	      if (
#ifndef SHARED
		  /* 'l' is always != NULL for dynamically linked objects.  */
		  l != NULL &&
#endif
		  __builtin_expect (l->l_flags_1 & DF_1_NODEFLIB, 0))
		{
		  const char *dirp = system_dirs;
		  unsigned int cnt = 0;

		  do
		    {
		      if (memcmp (cached, dirp, system_dirs_len[cnt]) == 0)
			{
			  /* The prefix matches.  Don't use the entry.  */
			  cached = NULL;
			  break;
			}

		      dirp += system_dirs_len[cnt] + 1;
		      ++cnt;
		    }
		  while (cnt < nsystem_dirs_len);
		}

	      if (cached != NULL)
		{
		  fd = open_verify (cached, &fb);
		  if (__builtin_expect (fd != -1, 1))
		    {
		      realname = local_strdup (cached);
		      if (realname == NULL)
			{
			  close (fd);
			  fd = -1;
			}
		    }
		}
	    }
	}

      /* Finally, try the default path.  */
      if (fd == -1
	  && ((l = loader ?: _dl_loaded)
	      /* 'l' is always != NULL for dynamically linked objects.  */
#ifdef SHARED
	      ,
#else
	      == NULL ||
#endif
	      __builtin_expect (!(l->l_flags_1 & DF_1_NODEFLIB), 1))
	  && rtld_search_dirs.dirs != (void *) -1)
	fd = open_path (name, namelen, preloaded, &rtld_search_dirs,
			&realname, &fb);

      /* Add another newline when we a tracing the library loading.  */
      if (__builtin_expect (_dl_debug_mask & DL_DEBUG_LIBS, 0))
        _dl_debug_printf ("\n");
    }
  else
    {
      /* The path may contain dynamic string tokens.  */
      realname = (loader
		  ? expand_dynamic_string_token (loader, name)
		  : local_strdup (name));
      if (realname == NULL)
	fd = -1;
      else
	{
	  fd = open_verify (realname, &fb);
	  if (__builtin_expect (fd, 0) == -1)
	    free (realname);
	}
    }

  if (__builtin_expect (fd, 0) == -1)
    {
      if (trace_mode)
	{
	  /* We haven't found an appropriate library.  But since we
	     are only interested in the list of libraries this isn't
	     so severe.  Fake an entry with all the information we
	     have.  */
	  static const Elf_Symndx dummy_bucket = STN_UNDEF;

	  /* Enter the new object in the list of loaded objects.  */
	  if ((name_copy = local_strdup (name)) == NULL
	      || (l = _dl_new_object (name_copy, name, type, loader)) == NULL)
	    _dl_signal_error (ENOMEM, name, NULL,
			      N_("cannot create shared object descriptor"));
	  /* Signal that this is a faked entry.  */
	  l->l_faked = 1;
	  /* Since the descriptor is initialized with zero we do not
	     have do this here.
	  l->l_reserved = 0; */
	  l->l_buckets = &dummy_bucket;
	  l->l_nbuckets = 1;
	  l->l_relocated = 1;

	  return l;
	}
      else
	_dl_signal_error (errno, name, NULL,
			  N_("cannot open shared object file"));
    }

  return _dl_map_object_from_fd (name, fd, &fb, realname, loader, type, mode);
}